1. Field of the Invention
The present invention relates to electrical cable terminations, more particularly, to controlled impedance cable terminations which are generally used to transmit high-frequency signals in electronic equipment.
2. Description of the Related Art
The purpose of a cable termination is to provide an interconnect from the cable to the electrical device and to provide a separable electrical interconnection between the cable and its operating environment. The characteristic of separability means that the cables are not interconnected by permanent mechanical means, such as soldering or bonding, but by temporary mechanical means.
Currently, controlled-impedance cables are terminated using a conventional type connector which is also controlled-impedance. Examples include an SMA (SubMiniature version A) connector or cables that are soldered to a printed circuit board (PCB) which is then separably connected to the working environment. The SMA connectors, while being generally the same impedance environment as the cable, have impedance mismatches which cause high-frequency attenuation at the point of interface between the cable and the connector and the connector and its working environment, such as like a PCB. Additionally, these cable terminations often require through holes in PCB's for mounting and, consequently, it can be difficult to design the best possible controlled impedance environment. These types of cable terminations are generally for a single cable and require a substantial amount of PCB area to terminate, thereby decreasing the density capability of connections.
Another form of prior art, disclosed in U.S. Pat. No. 7,544,093, is a system that employs removable cables that are held to the device by means of a spring. The cable has a terminal end which makes the signal conductor protrude from the cable terminal end. The terminal is then pressed to the device by means of a spring and the ground shield of the cable is connected to the device by a conductive rubber ground shield that shorts the terminal ground to the device ground.
Another issue with termination of coaxial cables is the expansion and contraction of the signal conductor and/or the insulator due to temperature excursions and/or cable flexure over time. The cables may need to be very precise and have a consistent electrical length in order to be useful in certain applications. The electrical length refers to the amount of time it would take an electrical signal to propagate the entire length of a cable. It is important that the electrical length be held consistent cable to cable through several flexure cycles or thermal excursions.
Furthermore, with cable terminations that employ compliant contacts, planarity of the cable center conductor and ground shield can be difficult to maintain through flexure or thermal excursions.